The uniqueness of the birth of Jesus was as prophesy in the book of Isaiah 9:6.The meaning of a virgin means, to be pure,undefiled, fresh and new. Mary was choosen for these reasons, for she was to be with child from the most Highest. A child who Himslef was pure, unsoilt and undefiled, and God wanted a woman of such purity to bring forth His Son, thus eliminating the risk of impurity.